303
Chapter thirteen: Disease
primarily with terrestrial pathogens. Listeria sp., a bacterium that causes food poisoning in
humans, was originally reported in abscesses in pinnipeds, based on the biochemical reactions of the bacteria. However, genetic tests revealed the organism to be Arcanobacterium, a
marine bacterium that does not cause disease in humans (Johnson et al. 2003).
Tests such as PCR and ELISA are often developed for terrestrial diseases. They may
cross-react with marine organisms but may make it difficult to tell from where the disease
originated. For instance, seals are susceptible to phocine distemper (PDV), a virus that causes
pneumonia and encephalitis, and is closely related to canine distemper virus (CDV). Initial
PCR testing showed these seals to be positive to CDV. While there is evidence that some outbreaks of seal distemper may have come from sled dogs with canine distemper, genetic testing revealed that PDV is genetically distinct from CDV (Mahy et al. 1988). Tuberculosis has a
similar story. The causative agent, Mycobacterium sp., can cause abscesses in the lungs, lymph
nodes, and throughout the body, and is zoonotic, meaning it can be spread from humans to
animals and back. Original tests of tuberculosis in sea lions described it as Mycobacterium
bovis, which often infects cows. It was not until genetic testing described a new strain,
Mycobacterium pinnipedii, that it was understood that the tuberculosis strain was unique to
pinnipeds—although it could still spread to other species from them (Cousins et al. 2003).
We have to take marine mammals’ unique physiology into account when analyzing
changes to blood work. Deep-diving cetaceans or pinnipeds may have a high percentage
of red blood cells (described as their hematocrit) in their blood, to carry extra oxygen as
they dive. If we compared their hematocrit to the normal values for a dog or a human, we
would think a healthy marine mammal might be dehydrated or have an abnormally high
hematocrit. It is important to know what normal blood values are for marine mammals, so
that we can correctly assess changes in animals with disease.
If a marine mammal is not hauled out on land, or stranded on a beach, it can be difficult to collect samples to diagnose disease. Lipophilic contaminants are stored in the
blubber layer, and a skin sample can give us information about the genetics of that animal,
and what population it belongs to. Collecting a skin or blubber sample from a whale at sea
involves using a dart gun to perform a remote biopsy, which collects a small tissue core
sample that can be analyzed. Imagine that, in addition to a moving animal target, you are
also bobbing up and down in a small boat.
Many of the medications used to treat marine mammal diseases are the same drugs as
those used in humans or other animals. Antibiotics are used to fight bacterial infections, antiinflammatories control inflammation and associated pain, and anesthetics provide sedation
for surgical procedures. However, unique adaptations to marine mammal physiology may
change the way drugs are metabolized in the body, translating to altered doses required for
treatment. For instance meloxicam, a non-steroidal anti-inflammatory drug (NSAID), is typically excreted from the body in roughly 24 hours in dogs and humans. A study in dolphins
showed elevated levels of meloxicam in the blood for more than 7 days, meaning that a onceweekly dose likely provides the same level of inflammatory relief in dolphins as a daily dose
in humans (Simeone et al. 2014). Dolphins are also more sensitive to the sedative effects of
some drugs, and benzodiazepines such as midazolam cause sedation at doses less than half
that required to sedate other terrestrial species (Dold 2014).
13.9 Lingering mysteries
Much of what is known with regard to the diagnosis and treatment of diseases in marine
mammals is due to studies that investigate the unique ways that marine mammals respond
to disease. However, many questions remain.
Chapter thirteen: Disease
primarily with terrestrial pathogens. Listeria sp., a bacterium that causes food poisoning in
humans, was originally reported in abscesses in pinnipeds, based on the biochemical reactions of the bacteria. However, genetic tests revealed the organism to be Arcanobacterium, a
marine bacterium that does not cause disease in humans (Johnson et al. 2003).
Tests such as PCR and ELISA are often developed for terrestrial diseases. They may
cross-react with marine organisms but may make it difficult to tell from where the disease
originated. For instance, seals are susceptible to phocine distemper (PDV), a virus that causes
pneumonia and encephalitis, and is closely related to canine distemper virus (CDV). Initial
PCR testing showed these seals to be positive to CDV. While there is evidence that some outbreaks of seal distemper may have come from sled dogs with canine distemper, genetic testing revealed that PDV is genetically distinct from CDV (Mahy et al. 1988). Tuberculosis has a
similar story. The causative agent, Mycobacterium sp., can cause abscesses in the lungs, lymph
nodes, and throughout the body, and is zoonotic, meaning it can be spread from humans to
animals and back. Original tests of tuberculosis in sea lions described it as Mycobacterium
bovis, which often infects cows. It was not until genetic testing described a new strain,
Mycobacterium pinnipedii, that it was understood that the tuberculosis strain was unique to
pinnipeds—although it could still spread to other species from them (Cousins et al. 2003).
We have to take marine mammals’ unique physiology into account when analyzing
changes to blood work. Deep-diving cetaceans or pinnipeds may have a high percentage
of red blood cells (described as their hematocrit) in their blood, to carry extra oxygen as
they dive. If we compared their hematocrit to the normal values for a dog or a human, we
would think a healthy marine mammal might be dehydrated or have an abnormally high
hematocrit. It is important to know what normal blood values are for marine mammals, so
that we can correctly assess changes in animals with disease.
If a marine mammal is not hauled out on land, or stranded on a beach, it can be difficult to collect samples to diagnose disease. Lipophilic contaminants are stored in the
blubber layer, and a skin sample can give us information about the genetics of that animal,
and what population it belongs to. Collecting a skin or blubber sample from a whale at sea
involves using a dart gun to perform a remote biopsy, which collects a small tissue core
sample that can be analyzed. Imagine that, in addition to a moving animal target, you are
also bobbing up and down in a small boat.
Many of the medications used to treat marine mammal diseases are the same drugs as
those used in humans or other animals. Antibiotics are used to fight bacterial infections, antiinflammatories control inflammation and associated pain, and anesthetics provide sedation
for surgical procedures. However, unique adaptations to marine mammal physiology may
change the way drugs are metabolized in the body, translating to altered doses required for
treatment. For instance meloxicam, a non-steroidal anti-inflammatory drug (NSAID), is typically excreted from the body in roughly 24 hours in dogs and humans. A study in dolphins
showed elevated levels of meloxicam in the blood for more than 7 days, meaning that a onceweekly dose likely provides the same level of inflammatory relief in dolphins as a daily dose
in humans (Simeone et al. 2014). Dolphins are also more sensitive to the sedative effects of
some drugs, and benzodiazepines such as midazolam cause sedation at doses less than half
that required to sedate other terrestrial species (Dold 2014).
13.9 Lingering mysteries
Much of what is known with regard to the diagnosis and treatment of diseases in marine
mammals is due to studies that investigate the unique ways that marine mammals respond
to disease. However, many questions remain.